Field of the Invention
The present invention relates to a planetary gear mechanism constituting a driving force transmission mechanism for transmitting a driving force from a drive source, and to a transmission provided with the planetary gear mechanism.
Description of the Related Art
Conventionally, a planetary gear mechanism having a sun gear, a pinion gear and a ring gear is available. For example, see Japanese Patent Publication No. 2013-181634 (Patent Document 1). At the center of the planetary gear mechanism, the sun gear as an outer-toothed gear wheel is arranged. The pinion gears as a plurality of small outer-toothed gear wheels mesh with the outer periphery of the sun gear at an equal interval. Further, the outer periphery of the pinion gear meshes with the ring gear as an inner-toothed gear wheel. A rotating shaft of the pinion gear is mounted to a frame referred to as a “carrier”. Due to this configuration, the planetary gear mechanism can change driving directions and gear ratios by inputting and outputting using the rotating shafts of the three gears, namely the sun gear, the pinion gear and the ring gear and by fixing the same.
A helical gear having oblique teeth is often used for a gear constituting the planetary gear mechanism. As the helical gear has a wide contact area, the helical gear advantageously transmits a large torque but generates a small noise.
However, when the helical gear is used, a load is applied in the axial direction of the rotating shaft (thrust direction) due to characteristics of the oblique-tooth wheel. Here, as the pinion gear and the ring gear are meshed with each other, a load is applied in the axial directions of the pinion gear and the ring gear. In this case, as the ring gear is fixed to the case of the planetary gear mechanism at an outer peripheral end of the planetary gear mechanism, a load is applied from the ring gear to the case on one hand, and a load is applied from the pinion gear to the carrier fixed in the axial direction on the other hand. In this way, if the ring gear is regarded as a system on the case, the carrier can be regarded as another system on the main shaft as the rotating shaft. Thus, one recognizes the planetary gear mechanism as a structure consisting of two different systems. The planetary gear mechanism consisting of two such different systems may fail to realize followingness of load transmission between these two systems, thereby causing a vibration or a noise.